1. Field of the Invention
The present invention relates to a method for driving plasma display panels (PDPs) which are used as display terminals for television sets and computers.
2. Description of Related Art
In recent years, the PDPs have been attracting much attention as large-sized flat displays capable of TV display in full color as their upsizing and adaptation to color display have been in progress. The PDPs are thought to be potential wall-mountable TV displays. For realizing such large-sized wall-mountable television displays, the PDPs are required to be further upsized, to provide images with higher definition, and also to exhibit a long-term stability in operation.
In general, AC-driven and DC-driven PDPs are known. The AC-driven PDPs are poorer in contrast and gradation compared with the DC-driven PDPs. However, the AC-driven PDPs have the advantages of a simpler structure, ability to generate images with higher definition, higher luminance and so on.
The PDPs are also classified into a surface discharge type and an opposition discharge type on the basis of the structure of electrodes. In the opposition discharge PDPs, a layer of a fluorescent material is formed directly on a discharge surface. For this reason, the opposition discharge PDPs have some disadvantages: They lack stability in operation; the fluorescent layer deteriorates in a short time due to ion impact during discharges and thereby the luminance drops, and the like. In the surface discharge type PDPs which are intended to eliminate these problems, electrodes for generating surface discharges are formed on a substrate and a fluorescent layer is formed on another substrate whereby the deterioration of the fluorescent layer can be prevented and a stable discharge characteristic can be obtained.
Among such PDPs, a surface discharge PDP having three kinds of electrodes is known as a typical AC-driven surface discharge PDP. The conventional PDP is now explained with the three-electrode surface discharge PDP as an example.
The three-electrode AC surface discharge PDP includes a panel having two glass substrates between which pixels, which are also referred to as "cells" or "discharge cells," are arranged in matrix. The pixel is defined by a pair of parallel sustain electrodes, which are also referred to as "display electrodes" or "main electrodes," covered with a dielectric layer and an address electrode, which is also referred to as a "select electrode" intersecting the sustain electrodes.
For driving the three-electrode AC surface discharge PDP, a time period for displaying one image is separated into an address period and a sustain period. This time period for display one image is referred to as a frame, a field if a frame consists of a plurality of fields, or a sub-field if a field consists of a plurality of sub-fields, and here referred to simply as a sub-field. The address period and the sustain period are each synchronous all over a screen. In the address period, an address discharge is generated to produce wall charge only on the sustain electrodes of specific cells. In the sustain period, a sustain discharge which is also referred to as display discharge is generated across the sustain electrodes on which the wall charge have been produced. In the address period, cells are selected by the address discharge across the select electrode and one of the sustain electrodes, and in the sustain period, the sustain discharge is generated across the sustain electrodes in the selected cells to display an image.
In such driving of the PDP, the addressing of specific cells is performed by a write address method or by an erase address method.
In the write address method, all cells on a screen are reset, that is, a "0" is written, at the beginning of each sub-field, then the address discharge is carried out only in selected cells, i.e., display cells, in the address period, and then the sustain discharge is carried out in the selected cells in the sustain period. In other words, at the beginning of each sub-field, all cells are initialized so that residual charge therein are reduced to zero. (To put it more precisely, a reset operation is performed to light all the cells to produce charge and then immediately erase the built-up charge.) Then the address discharge is generated only in the selected cells to produce wall charge therein, and then in the sustain period, the wall charge in the selected cells is maintained. This address discharge is called write address discharge.
On the other hand, in the erase address method, all cells are made to emit light, that is, a "1" is written, at the beginning of each sub-field, then the address discharge is carried out only in non-selected cells, i.e., cells not to be lighted for display, in the address period, and then the sustain discharge is generated in the selected cells in the sustain period. In other words, at the beginning of each sub-field, the wall charge is produced in all the cells, then the wall charge only in the non-selected cells is removed by the address discharge, which is called an erase address discharge, and then in the sustain period, the wall charge of the selected cells is maintained.
A three-electrode AC surface discharge PDP using the write address method is disclosed in Japanese Unexamined Patent Publication No. HEI 7(1995)-160218.
Three-electrode AC surface discharge PDPs using the erase address method are disclosed in Japanese Unexamined Patent Publication Nos. SHO 60(1985)-196797, SHO 61(1986)-39341, and HEI 8(1996)-101665.
In the above-described write address method, the residual charge produced in the sustain period of the immediately preceding sub-field is initialized and then the write address discharge is carried out. Accordingly, a priming effect of discharge cannot be utilized, and therefore a high writing voltage is required. Further, since the probability of discharge drops, a writing pulse must be lengthened. For this reason, there is a limit to high-speed drive for high-definition display. Further, a driver of high voltage resistance is needed, which raises production costs.
On the other hand, in the erase address method, since all the cells are made to emit light at the beginning of each sub-field, the contrast is somewhat poorer compared with the write address method. However, as merits outweighing this disadvantage, it is known that the priming effect of the wall charge can be utilized. Therefore, the address period can be shortened and a high-speed drive can be realized.
However, practical-use PDPs using the erase address method have not been positively developed so far for the following reasons. Even though a uniform voltage is applied to all the sustain electrodes, the discharge easily occurs in some cells, and hardly occurs in other cells. Due to such various voltage characteristics of the cells, it is difficult to produce wall charge uniformly in all the cells. Also the cells varies in thermal characteristics in producing the wall charge.